The GNSS has been considered the first choice for providing PNT services to telecommunications, power industry, and transportation applications because of its advantages of wide coverage, high accuracy, and low cost. However, the GNSS is inherently vulnerable to intended or unintended radio interference, and this threat has become more serious because of the easy availability of GNSS jammers on the market. From the robustness and safety perspectives, PNT services should not solely rely on GNSS. APNT solutions must be made available in the case of a GNSS outage. In this article, we investigate APNT solutions for aerial vehicles for which highly standardized PNT services are required to ensure secure and safe transportation, including solutions that have been proposed by the FAA in North America. We discuss the basic principle of each solution and analyze and compare their characteristics under different application scenarios. Finally, we conclude the article by predicting future trends in APNT solutions.